Bcl-6 expression and lactate dehydrogenase level predict prognosis of primary gastric diffuse large B-cell lymphoma

Background/Purpose The gastrointestinal tract is the most common site of primary extranodal non-Hodgkin lymphoma, and the prognostic factors of primary gastric diffuse large B-cell lymphoma (PG-DLBCL) differ in various studies. Methods We retrospectively searched for PG-DLBCL in a single institution, performed immunohistochemical analysis, classified tumor phenotype (Hans and Muris algorithms), reviewed medical records, and analyzed the clinical and immunophenotypic variables using Cox proportional hazard regression model. Results A total of 46 cases were identified including 25 males and 21 females with a median age of 63.5; 18 (39%) were at stage I and 28 (61%) at stage II. Seven (15%) patients underwent surgery as initial treatment including total ( n  = 3, 7%) and subtotal ( n  = 4, 9%) gastrectomy. Thirty-three patients (72%) received frontline chemotherapy treatment including ten with additional rituximab (MabThera) injection, and two (6%) of these patients developed perforation after chemotherapy. Four patients passed away shortly after diagnosis and the remaining three were lost to follow-up. The overall 2- and 5- year survival rates were 55% and 50%, respectively. The expression of various differentiation markers was CD10 (25%), bcl-2 (50%), bcl-6 (84%), and MUM1 (64%). Half of the cases studied (22/44) were classified as germinal center B-cell (GCB) phenotype and the remaining half as non-GCB according to Hans algorithm; 66% and 34% cases belonged to groups 1 and 2, respectively, according to Muris algorithm. Univariate analysis showed the expression of bcl-6 by the tumor cells as a favorable factor, while elevated serum lactate dehydrogenase (LDH) level, bcl-2 expression, and Muris group 2 were associated with poorer outcome. Multivariate analysis revealed that the two prognostic factors were bcl-6 expression and elevated LDH level, with hazard ratios of 0.09 ( p  = 0.002) and 3.72 ( p  = 0.024), respectively. Conclusion In this retrospective study with heterogeneous treatment modality, we identified bcl-6 expression and elevated LDH level as two prognostic factors for PG-DLBCL.